After lurking on this site for a while, I finally have something to add to the conversion.
I've been putting together a fermentation setup for a carboy using an office cooler. What I did was re-plump the hot and cold water tanks and connnect each of them to separate aquarium pumps. From the pumps the cold or hot water goes to copper coils that sit in a 12 gallon "Ice Cube" cooler, the water then returns to the tanks. The pumps are controlled by an Ebay aquarium temp controller.
Yesterday I finished putting it together and tested it out. The cooling side worked OK, it took six hours to cool eight gallons from 73 degrees down to 53 degrees. That's not very fast, but I think it's enough to keep up with the expected load. The hot side initially worked well, taking 40 minutes to raise the temperature from 61 to 75 degrees. Unfortunately, after a while I ran into a problem with the hot side pump, it lost it's prime and/or cavitated. I believe this is due to where I chose to mount the pump in relation to the location of the hot water tank, so I'll have to do some revisions.
Here's a picture without the copper coils or cooler - http://i229.photobucket.com/albums/ee276/s3pics/Office_Cooler.jpg